The uniqueness of gamma-crystallin as a specific marker of differentiation of lens fibre cells make this protein an interesting model for the study of control of differential gene expression in the normal and diseased state. The number of gamma-crystallin polypeptide chains is remarkably variable, not only among different species but within one lens as it passes from fetal to post-natal and then on to the adult life. This then presents a very attractive system where in the expression of different genes for a similar group of proteins is temporally and functionally regulated; the gamma-crystallins in the nucleus and in the cortex of the lens being different and expressed at different times. I propose to initiate studies in the human lens using gamma-crystallin as the specific protein marker of the lens fiber cell differentiation and gene expression. Gamma crystallin synthesis will be studied in vivo and in vitro cell free systems. Messenger RNAs will be isolated and characterized physically and functionally. Using recombinant DNA techniques, cDNA copies of the mRNAs will be cloned in bacterial plasmids; the naturally occurring gamma-crystallin gene sequences in the human genome will be identified, amplified through cloning in phage vectors and studied structurally by electron microscopy, restriction enzyme analysis and partial sequencing. Complete structure of a gamma-crystallin gene and the actual number of gamma-crystallin genes (and thus the basis of heterogeneity) will be determined. These studies will relate the primary structure of the protein to the arrangement of coding sequences within the genome and identify the controlling elements (sequences, e.g., promotors, regulators) present within or outside the natural gene(s) which may be involved in the precise regulation of the synthesis of different gamma-crystallin polypeptides in the different regions of the lens. Disruption in the normal progression of developmental events may result in a malfunctioning lens, and produce an opacity, or cataractous lens. The proposed project may suggest mechanisms leading to genetic bases for development of certain cataracts expressed in both early and late stages of life.